This invention relates generally to a method for inserting an insulation sheet into the slots of a stator core, more particularly to a method of inserting an insulation sheet used for insulating multi-phase coils from each other, which coils are wound around a stator core of an electric rotary device such as an electric motor. The invention also relates to an apparatus for carrying out such a method.
Generally, there are two primary ways of insulating stator coils. One of those ways is called "slot insulation" in which insulation sheets are placed in the slots of the stator core insulating the inside surfaces of the slots from the coil wires in the slots. The other way is called "phase insulation" wherein insulation sheets are partially inserted into certain slots insulating the coil of the first phase from that of the second phase.
A number of devices for achieving slot insulation have been developed. These devices automatically insert insulation sheets into the slots together with the coil wires. Some of these devices are used effectively in automated wire-inserting processes.
In contrast, phase insulation has typically been carried out manually. Automation of the phase insulation process is difficult because phase insulation requires handling of a very thin flexible insulation sheet which has a pair of parallel strap portions interconnected by a pair of connecting portions. Particularly, it requires that the insulation sheet is bowed into an arcuate shape and that the connecting portions are inserted into two predetermined slots to achieve proper positioning of the sheet. This tedious process results in a loss of productivity.
A phase insulation device which can solve the above-mentioned problem is disclosed, for example, in Japanese Patent Kokoku No. 59-39982. This device is illustrated in FIGS. 7 and 8. In FIG. 7, an insulation sheet 101 is held upright by a vacuum on a forming block 102. The forming block 102 is moved in the direction of the arrow Q from the position shown in FIG. 7 and sandwiches the sheet 101 between itself and upper and lower blocks 103 and 104. By this means, the sheet 101 is corrugated. A center clamp 105 is then lowered to temporarily hold the sheet 101 between the center clamp 105 and the upper and lower blocks 103 and 104.
Meanwhile, a piston 106, shown in FIG. 8, is activated to secure the opposite end portions of the sheet 101 to the positions between an upper side clamp 107 and the upper block 103 and between a lower side clamp 108 and the lower block 104. Subsequently, the forming block 102 is moved back to the initial position, and the connecting portions 101a of the sheet 101 are put into grooves 109a of pusher guides 109, respectively.
A stator 110 is positioned above the upper block 103, and it is lowered after the slots 111 are aligned with the pusher guides 109, as shown in FIG. 8. Then, pistons 113 in a tooling 112, as shown in FIG. 7, are extended until the pusher guides 109 abut the inside surface of the stator 110. This causes the sheet 101 to be stationary while the connecting portions 101a are brought into alignment with the respective slots 111 of the stator 110. After that, the center clamp 102 and the upper and lower side clamps 107 and 108 are loosened to release the sheet 101. Then, pistons 114 in the tooling 112 are extended and pushers 115 are moved through the pusher guides 109 toward the stator 110. This allows the connecting portions 101a to be inserted into the respective slots 111 through the slot openings 111a. By this means, the sheet 101 expands based on its own resiliency to conform to the inside diameter portion of the stator. The insertion process for the insulation sheet 101 is thus completed.
According to the conventional method, as mentioned above, an insulation sheet 101 is sandwiched at its intermediate portion by the center clamp 105 and the upper and lower blocks 103 and 104 and at its opposite end portions by the upper and lower blocks 103 and 104 and the upper and lower side clamps 107 and 108. A stator core 110 is then moved to the position around the sheet 101 after positioned correctly with respect to the sheet 101. Following this step, the pistons 114 in the tooling 112 are extended to push the connecting portions 101a in a radial direction so that the connecting portions 101a are inserted into the respective slots 111, which connecting portions have been held in the grooves 109a of the pusher guides 109. Because the pushers 115 for pushing the connecting portions 101a must be moved through the narrow slot openings 111a of the associated slots 111, they are provided at their leading ends with recesses to prevent the connecting portions 101a from slipping off of the leading ends. This arrangement indeed facilitates insertion of the connecting portions in a string-like configuration. However, it also means that it would be easy for the inserted connecting portions to dislodge from their respective slots.
One solution of the aforementioned problem is a new type of insulation sheet which has recently become available. This new insulation sheet is struck as a unitary piece from such insulating sheet material such as nylon, polyester or other similar material. The sheet has connecting portions and body portions which are integrally formed with the connecting portions. The width of each connecting portion is greater than that of the opening of the associated slot so as to inhibit accidental disengagement of the connecting portions from the associated slots. However, such connecting portions have a greater width and are difficult to fit in the recesses of the pushers. Thus they tend to escape from the leading ends of the pusher during insertion process. Furthermore, such connecting portions could be ruptured as a result of being pressed against the opposite side edges of the leading ends. For these reasons, automation of insertion process for this new type sheet is again very difficult and no apparatus for automatically carrying out such a process has yet become available.
With the previously described apparatus, the insulation sheet is gripped at both its intermediate portion and at its opposite end portions. Then the pusher guides are moved forward to trap the sheet between the pusher guides and the inside surface of the stator. This machine therefore is useful only with those insulation sheets having their connecting portions at the positions spaced inwardly from the opposite end portions thereof and is not useful with the sheets with their connecting portions at the opposite ends thereof.
Also in the previously described apparatus, the insulation sheet is held vertically at the outset by the forming block. This step is difficult to automate, and therefore it must be accomplished either manually or by an extremely complicated automatic sheet dispenser.
An object of the present invention, therefore, is to provide a method of inserting into predetermined slots a one-piece insulation sheet having the connecting portions at the opposite ends thereof. A second object of this invention is to provide an apparatus which will automatically carry out such a method.